The objective of the project is to study the mechanisms of action of parathyroid hormone (PTH) focusing primarily on the role of cAMP, and the development of a bioassay based on stimulation of adenylate cyclase from osseous tissue. For establishing the PTH bioassay based on stimulation of osseous tissue adenylate cyclase, we propose to characterize the adenylate cyclase of the highly responsive osteosarcoma clone (ROS 17/2) with respect to: optimum assay conditions for maximizing hormone response (MgATP2-, Mg2ion, GTP) and compare effects of PTH from various species as well as synthetic PTH fragments and analogs. We propose to investigate the role of the previously dscovered adenylate cyclase enhancing cytosol factor (Egan et al., BBRC 80:176-182, 1978) on hormone stimulation of the enzyme using: (1) responsive and non responsive clones and (2) the parallel in vivo inducibility of cytosol factor and hormone response, as experimental tools.